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Measuring Vegetation
Characteristics
Going beyond land cover
Vegetation characteristics
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Some commonly measured characteristics:
 Vegetation structure
 Phenology
 Primary productivity
 Leaf area index
 Vegetation health/vigor
Research is ongoing to improve existing indices and create new
ones and to tie these assorted indices to useful
environmental/ecological processes
Some indices are created in a production environment on a
global scale and others are created on a case-by-case bases
Measurement of these indices is based on the fact the
reflectance, transmittance, and scattering of energy in a canopy
is greatly affected by vegetation structure and how vegetation
components (leaves, branches, trunk) interact with the
wavelength(s) of energy used by a particular instrument
Vegetation indices
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Uses the fundamental
principle that chlorophyll in
green healthy vegetation
largely absorbs red and blue
wavelengths of light and
strongly reflects nearinfrared wavelengths
Closely related to primary
productivity
Dozens of vegetation indices
have been developed
Often composited for
periods ranging form 8 days
to one month
Often used to monitor
changes in productivity over
time
Band 3 (Red)
Band 4 (near-IR)
RGB image
NDVI
Popular vegetation indices
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Normalized Difference Vegetation Index (NDVI)
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NDVI = (NIR – Red) / (NIR + Red)
Most common vegetation index
Value is always between +1 and -1 with green
vegetation closer to +1 and no vegetation close to
0
Negative values are possible for non-vegetated
features
Somewhat sensitive to radiometric contaminants
Popular vegetation indices
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Enhanced Vegetation Index (EVI)
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Developed to improve upon NDVI
Output as a standard MODIS product
EVI = G*[(NIR-Red)/NIR+C1*Red-C2*Blue+L)] where G,
C1, C2, and L are coefficients:
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G = Gain factor (2.5 for MODIS)
L = Canopy background adjustment (1 for MODIS)
C2 = Atmospheric aerosol resistance (6 for MODIS)
C2 = Atmospheric aerosol resistance (7.5 for MODIS)
These coefficients reduces atmospheric effects in the red
band and compensates for the different ways in which
near-IR and red light behaves inside and below a canopy
thereby reducing the effect of soil type, soil moisture,
surface litter, and snow cover.
EVI is more sensitive to canopy structure than NDVI
Continuous fields data
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Each pixel provides a proportional estimate of
woody vegetation (needleleaf or broadleaf and
evergreen or deciduous), herbaceous vegetation,
and bare ground
A standard MODIS product available for the globe
(except the poles) at a resolution of 500 meters
Initial reports are quite positive on the utility of
this layer for species distribution models
Use of active sensors to measure
vegetation characteristics
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Radar and lidar are used to measure vegetation
structure characteristics such as:
 Height
 Density
 Timber volume
 Canopy volume
 Biomass
This is an area of active research and additional
indices will certainly be developed and more
sophisticated instruments will be developed during the
next several years